In recent years, expectation for electric vehicles or hybrid electric vehicles has increased because of the global environmental problems. For rechargeable batteries as the power supply of those vehicles, both reduction in the size and weight and increase of the capacity and output are demanded. Thus, a battery pack in which a plurality of batteries formed by cells are connected in series is used as the power supply. Moreover, a battery pack in which, in order to cool respective batteries, the batteries are arranged in parallel in a case and a cooling air from the vehicle interior is introduced into the case is known from Japanese Patent Laid-Open Publication No. 2001-319697, for example.
Referring to FIG. 8, a plurality of batteries 21 are arranged in parallel in a case 22 with a pitch that allows an appropriate ventilation gap to be formed between the adjacent batteries 21. In the case 22, cooling-air passages 23 and 24 are formed on both sides of the array of the batteries 21, respectively, and a cooling-air inlet 25 and a cooling-air outlet 26 are provided at one end of the cooling-air passage 23 and at the other end of the cooling-air passage 24, respectively.
The case 22 mentioned above is accommodated and secured in a battery box (not shown) which has a fan provided at a position opposed to the cooling-air inlet 25. Cooling air W delivered by the fan enters the cooling-air passage 23 of the case 22 from the cooling-air inlet 25, flows through the ventilation gap between the batteries 21 and the cooling-air passage 24, and is then discharged from the cooling-air outlet 26. The cooling air W cools the respective batteries 21 while flowing in the case.
However, in a case where the aforementioned battery pack is mounted in an electric vehicle or hybrid electric vehicle, air taken from the vehicle interior is introduced into the case 22 as the cooling air W, and the cooling air W of which the temperature has been increased by cooling the batteries 21 is discharged to the outside of the vehicle. Therefore, if the battery pack falls into abnormal state and gas is discharged into the case 22, the gas within the case 22 flows back into the vehicle interior when the fan stops.
Therefore, the present invention was made in view of the aforementioned problems of the conventional techniques, and aims to provide a battery pack that prevents gas discharged due to a trouble in a battery from flowing back through a supply passage of cooling air and prevents a trouble caused by the reverse flow of the gas.